| March 5, 2003 NASA-Funded Research Looking at El Niño Events to Forecast Western U.S. Snowfall A NASA-funded study uses a computer model to understand an observed link between winter and spring snowfall in the Western U.S. and El Niño Southern Oscillation. Almost 75 to 85 percent of water resources in the Western U.S comes from snow that accumulates in the winter and early spring and melts as runoff in spring and summer. Understanding this connection and using it to predict future snowfall rates would greatly help both citizens and policy makers. One of the missions of NASA's Earth Science Enterprise (ESE), which funded this research, is to better understand how the Earth system is changing. Within this framework, NASA is committed to studying variability in the water cycle, how well we can predict future changes in the earth system and the consequences of change in the Earth system for human civilization. Lead authors Jiming Jin and Norman Miller of the U.S. Department of Energy's Lawrence Berkeley National Laboratory, Berkeley, Calif., in collaboration with Soroosh Sorooshian and Xiaojang Gao at the University of Arizona, Tucson, find that higher and lower tropical Pacific sea surface temperatures (SSTs) that characterize El Niño and La Niña change atmospheric wind patterns in the mid-latitudes in winter and spring, shift the way moist air gets transported in the atmosphere, and directly affect Western U.S. precipitation and snow accumulation. El Niño / Southern Oscillation (ENSO) marks a see-saw shift in surface air pressure between Darwin, Australia and the South Pacific Island of Tahiti. When the pressure is high at Darwin it is low at Tahiti and vice versa. El Niño, and its sister event La Niña, are the extreme phases of this southern oscillation, with El Niño referring to a warming of the eastern tropical Pacific, and La Niña a cooling. By better understanding the connections between these processes, scientists can update their computer climate models to improve their ability to forecast future snowfall and water availability in the west. "If the computer climate models can accurately describe the processes that connect ENSO and snowpack in the Western U.S., then the model can be used to predict the impact of ENSO on snowfall in those areas," said Jin. "In addition, the model can give us more detailed information than observations, which can lead to a further understanding of those observed processes." The researchers entered over 45 years of data from 1949 to 1995 into their computer climate model. They included observed global sea surface temperatures, wind data, the amount of water contained in snowpack for the beginning of the first four months of each year from over 300 western U.S. field sites, and precipitation and surface air temperature observations. They also used NASA-derived Normalized Difference Vegetation Index (NDVI) data for improved model predictions. NDVI measures the amount of solar energy reflected and absorbed by vegetation. NDVI was created by Compton Tucker of NASA Goddard, using data from the National Oceanic and Atmospheric Administration's (NOAA) Geostationary Environmental Orbiting Satellite (GOES) Advanced Very High Resolution Radiometer (AVHRR) instrument. The data used in this research also comes from the Moderate Imaging Spectroradiometer (MODIS) instrument aboard NASA's Terra satellite. During the weak ENSO episodes, Washington, Oregon, Idaho, and Montana experienced decreased precipitation during weak El Niños, and increased precipitation during the opposite La Nina phase. During the strong El Niño episodes, stronger winter and spring precipitation was found south of Sacramento, including parts of California, Nevada, Utah, Colorado and all of Arizona and New Mexico. However, during strong La Niña events, the researchers did not find any changes to precipitation patterns in the western U.S. The model matched well with actual observations except when it came to weak ENSO episodes, including both El Niño and La Niña. During those events, the mid-latitude atmosphere in the model reacted too strongly to the shifts in tropical Pacific SSTs, and moist air masses from that region moved incorrectly. Still, it shows that different intensities of ENSO episodes have differing affects on western U.S. snowfall. The researchers hope to fine-tune the model's responses in the future. This research may yield a forecast tool that greatly benefits citizens and water resource managers in the Western U.S. Jin and Miller are currently developing new snow assimilation techniques that show improved forecast skill, which they hope will make water allocation decisions more accurate and cost efficient. These findings were presented at the 83rd Annual Meeting of the American Meteorological Society in Long Beach, Calif. This research was funded by NASA's ESE Interdisciplinary Science and Applications Programs. The Applications Division applies the results of the nation's investment in ESE to issues of national concern, such as environmental quality, resource management, community growth, and disaster management to support policy makers at the state and local levels. ###
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Editor
University of Arizona
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American Meteorological Society
(Phone: 425/432-2192) | |
 Snowpack and Runnoff Snowpack is determined by wind, air temperature, storm frequency, and the amount of moisture in the atmosphere, and how wet the soil is before the first snowfall, help define the snowpack. Snowpack becomes more dense as it deepens the lower layers are compressed. Density and compression also define it. Wet snow has a higher density and produces more water than dry, powdery snow. Compression affects the crystalline structure of the snowpack. Density and crystalline structure of snow affect how fast the snowpack melts and how much water it yields. Air temperature and availability of atmospheric moisture determine how wet or dry the snow is. CREDIT: National Water and Climate Center  The Colorado River The Colorado and Columbia Rivers both begin in high mountain country. The Colorado serves large population centers in southern California and Arizona. Along the river, a number of storage facilities were constructed to capture snowmelt water and produce electricity, irrigate farms, supply water to cities and towns, and prevent floods. Multi-state agreements regulate the quality and quantity of streamflow on the Colorado River. CREDIT: National Water and Climate Center, U.S. Dept. of Agriculture  Wet and Dry Snow: the Difference in Water Content Wet snow has a higher density and produces more water than dry, powdery snow. Typically, the west slope of the Cascade Mountain Range (in the Columbia River Basin), in response to the Pacific Ocean's strong influence, receives heavy, wet snow. One foot of that snow, newly fallen, can produce up to 1.5 inches of water. In other areas, such as the Wasatch Mountains in central Utah, the snow is much drier. It is light and powdery -- excellent for skiing -- and 1 foot of fresh snowpack might contain only an inch of water. Pictured is Mount Rainier in western Washington State. The flanks of Mount Rainier are drained by five major rivers and their tributaries: Carbon, White, Cowlitz, Nisqually, and Puyallup. The Cowlitz joins the Columbia River in the southwestern part of the State to flow to the Pacific Ocean. CREDIT: USGS, Lyn Topinka, 1975  Columbia River gorge This is a photograph taken along the Columbia River Gorge, at the southern edge of the Gifford Pinchot National Forest. The Forest is located in southwest Washington State, and now contains 1,312,000 acres and includes the 110,000-acre Mount St. Helens National Volcanic Monument established by Congress in 1982. Because snowpack is a major water resource in the Western U.S, an accurate forecast of snow amounts is essential to managing the water supply in that region. This research looks at how El Niño/Southern Oscillation cycles could be used as a factor to predict snowpack evolution in the Columbia and Colorado River basins. CREDIT: Roger Peterson, US Forest Service, Gifford Pinchot National Forest  Map of the Colorado River Basin States in the Colorado River Basin include parts of Wyoming, Colorado, Utah, Arizona, New Mexico, Nevada and California, all of which are competing for water from the Colorado River.
The river is one of the most regulated and managed U.S. rivers, providing water to over 17 million people and more than one million acres of farmland in Arizona, California, and Nevada. Along the river, hydroelectric plants generate about 12 billion kilowatt-hours of electricity annually. CREDIT: The Arizona Dept. of Water Resources  Map of the Columbia River Basin The Columbia River carved the Interior Columbia River Basin from the landscape of seven Western states and two Canadian provinces. The river itself flows from its headwaters in British Columbia, Canada through only two states, forming part of the Washington-Oregon border, the vast Interior Columbia River Basin is defined by the area drained by the river and its many tributaries. This 58-million-hectare area (about the size of France) extends roughly from the crest of the Cascade Mountains of Oregon and Washington east through Idaho to the Continental Divide in the Rocky Mountains of Montana and Wyoming, and from the headwaters of the Columbia River in Canada to the high desert of northern Nevada and northwestern Utah. CREDIT: U.S. Army Corps of Engineers, North Pacific Region |
